This invention relates to a hard alloyed powder of a multiple boride comprising iron in which a part of iron boride is substituted by a non-ferrous boride or multiple boride such as Cr, Mo, W, Ti, V, Nb, Ta, Hf, Zr, Co and Ni, and to a method of making such hard alloyed powder.
The cemented carbides, especially materials comprising tungsten carbide as a hard phase, have hardness and strength and they have been broadly used for metal cutting tools, metal molds and the like.
However, tungsten, a main element of cemented carbide, is becoming increasingly scarce and therefore the cost of this raw material is very high.
Further, the specific gravity of the cemented carbides are as high as 13 to 15.
Moreover, the cemented carbides are very poor both in corrosion resistance and oxidation resistance at high temperature.
On the other hand, the Stellite Co base alloy comprising W and Cr, has good corrosion resistance and high oxidation resistance, but is poor in hardness and wear resistance. In order to improve corrosion resistance, oxidation resistance at high temperature, high specific gravity, high cost of raw materials and so forth, we had proposed a sintered hard alloy, prepared from a hard alloyed powder comprising iron boride or iron multiple boride in which a part of iron boride is substituted by a non-ferrous boride or multiple boride. See for example U.S. Pat. No. 3,999,952.
Improved corrosion resistance, oxidation resistance at high temperature, low specific gravity and low cost of raw materials were attained but the sintered hard alloy of said patent did not have strength comparable to the cemented carbides.
This is mainly due to the nature of the hard alloyed powder which is main raw material of the sintered hard alloy.
We found that the inclusion useful boride-forming elements such as Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Co and Ni, in this hard alloyed powder, make the sintered hard alloy stronger and harder. In contrast, Al, oxygen and C in small amounts in the hard alloyed powder, make the hard alloyed powder brittle, with the result that the sintered alloy becomes poor in strength.